1. Field of the Invention
The present invention relates to an optical switch which is provided in an optical communication system.
2. Description of the Background Art
An add-drop multiplexer (ADM) disclosed in Japanese Patent Application Publication No. 11-271559 is known as an optical device using an optical switch. The ADM is equipped with an input port waveguide, an optical demultiplexer, an optical multiplexer, and an output port waveguide on the substrate. The output port of the optical demultiplexer and the input port of the optical multiplexer are connected with waveguide paths. The waveguide paths include an optical multi-port switch that adds or drops signal light, or performs both.
A thermo-optic switch consisting of a Mach-Zehnder (MZ) interferometer is used for the optical switch. The thermo-optic switch has a heating element, which controls the optical path length (phase shift) of an arm of the MZ interference meter. The thermo-optic switch drops signal light from the optical demultiplexer and adds different signal light to the optical multiplexer, by applying an electric current to the heating element. On the other hand, in the condition in which no electric current is applied to the heating element, the thermo-optic switch outputs signal light from the optical demultiplexer into the optical multiplexer.
In the case of using a thermo-optic switch consisting of the MZ interferometer for an optical switch as in the case of the ADM, it is necessary to provide an optical path of corresponding length to achieve the desired phase difference. Therefore, the optical switch becomes large, and the ADM is large-sized as a whole. The operating speed of the ADM as an optical switch is slow (10 ms or more) because it uses the modulation of the refractive index due to the temperature variation (heating by heating elements). Moreover, in the ADM, in order to achieve uniform switching characteristics for a plurality of optical switches, it is necessary to adjust the amount of voltage to be applied to the heating elements. Consequently, the productivity is inferior.
An ADM using another type of optical switch is disclosed by M. Katayama et al. Proc. Optical Fiber Conf. Anaheim, 2001 WX4-1. The optical switch is equipped with a substrate on which a first waveguide path and a second waveguide path are provided such that they intersect each other, a trench having a depth which is as deep as to expose the whole end face of the first waveguide path and the second waveguide path at the intersecting part thereof, and a driving means which retains an optical element and moves them to an advancing direction and a retreating direction relative to the optical paths of the first waveguide path and the second waveguide path.
It is an object of the present invention to provide an optical switch in which cross talk is improved.
In order to achieve this object, the optical switch according to the present invention is provided with a substrate, a first waveguide path provided on the substrate, a second waveguide path that is provided, intersecting the first waveguide path, on the substrate, a trench which is as deep as to expose the whole end face of the first waveguide path and the second waveguide path at the part where they intersect each other, an optical element, and a driving means which moves the optical element in an advancing direction and a retreating direction relative to the optical path of the first waveguide path and the second waveguide path, wherein the first waveguide path and the second waveguide path are arranged such that their central axes are positioned at different angles at the part adjacent to the trench, with respect to a straight line extending in an orthogonal direction relative to the side face of the trench.
In one embodiment, the optical switch may have a driving means that retains the optical element in a space defined by the trench and moves them to an advancing direction and a retreating direction relative to the optical paths of the first waveguide path and the second waveguide path. The first and second waveguide paths may be formed such that their width is larger at the portion that faces the trench than at other portions.
The present invention is further explained below by referring to the accompanying drawings. The drawings are provided solely for the purpose of illustration and are not intended to limit the scope of the invention.